"Mushroom" is a generic term which refers to a number of species of fungus, in particular those species which are edible. Mushroom growing has become a multi-billion dollar international industry in recent years. The industry has pushed hard and long to attempt to discover methods of growing bigger, more esthetically pleasing, and tastier mushrooms. It has also been a prime object of the industry to discover methods of growing these mushrooms in the shortest possible period of time and with the least incidence of diseases and failures.
A typical mushroom crop consists of a number of distinct stages. The mushroom must go through the stages of compost preparation, compost pasteurization, spawn preparation, planting, vegetative development, after which time the environment is "cased" to induce the production of fruit, and finally, fruition. The length of time required for each of these stages is dependent both upon the type of mushroom to be grown and upon the precise environmental conditions to which the mushroom spores and mycelia are exposed.
The production of the mushroom spawn for innoculation is one of the initial stages. Typically, this consists of the preparation of a large number of kernals of some member of the wheat family, preferably rye, although millet is also used. The rye kernals are sterilized and prepared and then innoculated with the mycelia of the particular species of mushroom desired, typically, in the United States, Agaricus bisporus. The mushroom mycelia are then allowed to proliferate upon the kernels of grain until the individual kernels are completely covered by the living mushroom tissue. The mushroom mycelia-covered kernels which result are known in the industry as "spawn".
The production of spawn is typically carried out in a commercial laboratory environment. The sources for mushroom spawn, particularly those of a specific species, are quite limited. Ordinarily, the spawn available for a particular type of mushroom will have less than fifty original sources throughout the world. Sterility and quality control in the early stages of spawn production are extremely important. Consequently, the spawn is typically produced in a laboratory then stored and shipped to the end users, the growers.
Once the grower has received the spawn he is ready to undertake the second stage of mushroom growing, the planting of the spawn. The grower has prepared, and aged to the proper stage, under proper temperature and environmental conditions, a bed of compost in which the spawn is to be planted. This compost has traditionally been the cleanings from horse stables or other similar composts, although modern composts come from a variety of sources. It is necessary to select and treat the compost carefully so that it has good nutrient content and does not contain undue amounts of acid or various chemical and biological inhibitors such as high ammonia content. High concentrations of chemicals such as acids or ammonia will hinder the growth of the mushrooms and reduce the efficiency of the operation.
The actual planting consists of distributing the spawn throughout the compost bed in such a manner that the food contained in the bed is reasonably accessible to each spawn. To achieve this, the spawn grains are typically evenly distributed over the compost surface and then mechanically mixed into the compost.
Once the spawn has been planted, it is allowed to vegetate and grow under controlled environmental conditions until it is "cased" and then continues to vegetate until the mycelia are ready for fruition. The amount of time necessary for such vegetative growth is dependent on the precise environmental conditions, the particular type of mushroom and the nutrative content of the compost bed. A typical vegetative stage extends between thirty days and thirty-six days.
After the vegetative phase has continued for the appropriate length of time, approximately twelve to sixteen days, the grower will perform an operation known as casing. Casing involves spreading a thin layer of soil over the compost bed. This soil is kept moist. The bed temperature is thus reduced for a short period. This temperature reduction has the effect of causing the mushroom mycelia to fruit or "crop" and thus send up the actual mushrooms through the casing soil.
The final stage of a mushroom crop is the actual fruition or "cropping". During this stage the mature fungus sends up the fruiting bodies which are marketed as mushrooms. Each particular colony of fungus will send up fruit when it has reached the proper stage. The actual time frame of the fruition varies throughout the bed. The fruition stage of the crop typically appears about nineteen days after casing and lasts for approximately four to five weeks.
Of the four main stages of a mushroom crop only the vegetative stage and the fruition stage are significantly affected by the addition of a nutrient additive. The duration of the spawning stage is determined primarily by the type and condition of grain used and the particular strain of mushroom mycelia innoculated onto the grain. The planting stage is of relatively short duration and can be improved only by mechanical techniques such as improved evenness of distribution of the spawn kernels. The timing of the casing affects the timing of the fruition but this operation is relatively independent of nutrients. The vegetative and fruition stages, however, and to a certain extent the later portions of the spawning stage, can be affected significantly by the addition of biological activators and nutrients to the process.
The basic methods for producing mushroom spawn have been described in a number of United States patents. These patents include U.S. Pat. No. 1,869,517 issued to J. Sinden; U.S. Pat. No. 2,005,365 issued to R. DiGiacinto; U.S. Pat. No. 2,044,861 issued to J. Sinden; and U.S. Pat. No. 3,828,470 issued to B. Stoller. Each of these references relates to the manner in which mushroom spawn is prepared for the vegetative phase.
U.S. Patents have also issued regarding the method of adding nutrients or synthetic composts to mushroom cultures to provide for improved growth characteristics. These have included U.S. Pat. No. Re. 22,202 reissued to B. Stoller; U.S. Pat. No. 3,560,190 issued to D. Hughes, et al.; and U.S. Pat. No. 3,942,969 issued to A. Carrol, Jr., et al. Each of these patents relates to the specific content of additives to either the spawn or the compost bed. The additives and processes involved in these references are intended to increase the production of mushrooms and/or decrease the period of time necessary to grow the mushrooms under certain conditions.
The subject of mushroom growth activation has also been treated in a number of scientific articles. These include "Stimulation Of Yield In The Cultivated Mushroom Via Vegetable Oils" L. C. Schisler, APPLIED MICROBIOLOGY, July, 1967, pages 844-850; "The Lipids Of Thermophilic Fungi: Lipid Composition Comparisons Between Thermophilic and Mesophilic Fungi" R. O. Mumma, et al, LIPIDS, January, 1970, Volume 5, No. 1, pages 100-103; "Thermophilic Fungi: II." R. O. Mumma, et al., LIPIDS, Volume 6, No. 6, pages 584-588 (1971); "Thermophilic Fungi: III" R. O. Mumma, et al, LIPIDS, Volume 6, No. 8, pages 589-594 (1971); a masters thesis entitled "Studies On Lipid Metabolism Of Agaricus Bisporus (Lange) Sing. and Compost Lipid Composition" by David E. Smith, Ohio State University (1975); and "Lipid Metabolism Of Mushroom Mycelia" R. Barry Holtz & David E. Smith, MUSHROOM SCIENCE 10, Part 1, pages 437-444 (1979)
The various prior art methods have indeed succeeded in producing higher quality mushrooms in a shorter period of time than the older methods. However, there remains a great deal of room for improvement.
Even a small improvement may result in a substantial increase of production to a mushroom grower. For example, a shortening of the vegetative period by as little as two days will allow the grower to produce an entire extra crop in under three years. Thus, improvements in the mushroom techniques and additives are of particular commercial importance.
The prior art attempts have, in some degree, been aimed at improving the nutrient environment for the mushroom mycelia during the vegetative stage. These have included preparing more readily digestible food stuffs for the mushroom mycelia and have extended to the use of delayed release nutrients. However, none of the prior art attempts has directly attacked the phenomenon of aging within the individual mushroom cells and the concomitant slowing of metabolic membrane transport mechanisms which can effect the growth velocity.